What is it?

Neonatal mastitis is a localized cellulitis of the breast tissue. It may be accompanied by an abscess. Most cases are seen in infants <2 months of age. With the peak approximately 2 weeks of life (the peak age for abscess is a little older at 4 weeks).  They are actually rarer in preemies, probably because the breast tissue has had less time to be exposed to anaerobes. Males and females are equally affected under 2 weeks of age, but more females will be diagnosed after that.

Most often the infection spreads from the skin, and as you’d expect the predominant pathogen is Staphylococcus aureus. You may also see gram negatives, which can spread systemically. These less common bugs include Escherichia coli, Salmonella, anaerobes and group B Streptococcus.

50% of infants with mastitis develop abscesses

The key feature on physical exam is fluctuance. Only 20% of cases will have purulent nipple discharge. Ultrasound is the most useful imaging modality.

Mastitis is almost always unilateral. Key clinical features include erythema, swelling and tenderness. The ipsilateral axillary lymph nodes may be swollen. it actually does not spread all that often. In a review of cases of neonatal mastitis Montague et al noted that  only ¼ had fever, 43% irritability and 14% decreased oral intake. So, most often, the infant will be relatively well appearing with unilateral breast swelling.

What’s the workup?

The diagnosis is suspected clinically, but labs can be helpful to evaluate risk and guide treatment. So, in the well appearing infant you should get a CBC and Blood Culture. If there is purulent drainage obviously get a culture. Breast ultrasound can help identify abscesses.

Do I need to do an LP or not?

It depends on whether or not the infant is ill-appearing. If they look systemically ill then yes. if not, then generally an LP is not necessary – nor is urinalysis and culture. Remember that the blood/urine/CSF triad is for fever of unknown source. If the baby clinically has mastitis and fever then the source is pretty much apparent right? However, if the baby looks ill, or the WBC is high (>15,000) then consider a more broad workup including urine and CSF. The issue of what to do with fever + mastitis isn’t necessarily solved by the literature. Ultimately, the choice is yours, but in a febrile baby with mastitis under 21-28 days of age you need a darn good reason to NOT perform the LP. Don’t try to talk yourself out of doing the LP if you’re on the fence either. Just do it.

What’s the treatment?

Antibiotics – specifically ones directed towards the most likely pathogen. As noted previously this is most often S. aureus, and that generally means MRSA. There are no randomized controlled trials for the treatment of neonatal mastitis. Supportive care for any patient includes warm compresses and acetaminophen for pain and fever. Parents should not squeeze the breast in an effort to express pus.


Admit those under 2 months of age on IV antibiotics

  • Clindamycin
  • Nafcillin (if you do not suspect MRSA)
  • Vancomycin


After obtaining urine and CSF studies you’ll want to treat with multiple drugs. options include:

  • Vancomycin + nafcillin + ceftriaxone or cefotaxime
  • Vancomycin + nafcillin + gentamicin

Drainage of abscesses

I&D is warranted if there is not spontaneous drainage. I will not drain a breast abscess, especially in a newborn female. You should always consult pediatric surgery/gynecology. You run the risk of breast hypoplasia and scarring even with a successful I&D.


Montague EC, Hilinski J, Andresen D, Cooley A. Evaluation and treatment of mastitis in infants. Pediatr Infect Dis J. 2013 Nov;32(11):1295-6. doi: 10.1097/INF.0b013e3182a06448.